About to open up another can of worms here, as I a sure the GG people pro and con will pop in. Many of us have used different devices to help us with trimming, throwing and other things in the studio. Heck I remember a thread not too long ago with a home made vertical slab roller. Right now there is a great thread going on about using laser pointers as a throwing aid for repetitive sizing of pieces. With the cost of laser pointers so low-makes sense.
So I will start this off with a simple contribution, a trimming chuck made of common plumbing parts that can be used for a very specific type of trimming I have always had problems with-chalice stems. This is made up of 3" pieces, Pipe flange, pipe, pipe hub donut, and tank to bowl gasket. The gasket is very soft, but firm. This allows the stems to be inserted into the assembly and trimmed without marking or damage. You may not throw chalice stems, but if you throw bottles, you might want to give it a try. If you want more information, try my blog.
So what do others of you have to offer in the way of studio tip, throwing aid or other tool for the studio?